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Pd-Au and Pd-Pt catalysts for the direct synthesis of hydrogen peroxide in absence of selectivity enhancers

Paper ID Volume ID Publish Year Pages File Format Full-Text
40248 45848 2013 15 PDF Available
Title
Pd-Au and Pd-Pt catalysts for the direct synthesis of hydrogen peroxide in absence of selectivity enhancers
Abstract

•Performance of Pd, Au/Pd and Pt/Pd catalysts supported on K2621.•Catalysts tested with no selectivity enhancer in the DS under batchwise condition.•The productivity of hydrogen peroxide is very little sensitive to the amount of gold.•Addition of a small amount of Pt and Au makes the catalysts less active than 1% Pd.•Selectivity raises up to 60% with the addition of the second metal to the catalyst.

Organic polymers are suitable candidates as catalytic materials for the direct synthesis of hydrogen peroxide (DSR) from dihydrogen and dioxygen, in view of the low temperature applied. In particular, strongly acidic ion-exchange resins have been already proposed for this reaction, either as carriers of PdII ions or Pd0 nanoparticles, but not for bimetallic Pd/Pt and Pd/Au catalysts, which are also active in this reaction. The introduction of PdII, PtII and AuIII precursors into the commercial ion-exchangers Lewatit K2621 and their subsequent reduction with an aqueous formaldehyde solution produced a library of bimetallic catalysts with 1% Pd (w/w) and a variable content of either Pt (0.1–1%, w/w) or Au (0.25–1%, w/w). The catalysts were tested with no selectivity enhancer in the DSR under batchwise condition at 2 °C in MeOH at 2 MPa, with a CO2/O2/H2 (72/25.5/2.5) mixture. In the Pd-Pt catalysts the addition of the smallest amount of Pt (0.1%, w/w) gave the best results in terms of the initial selectivity (43%) and the top concentration of H2O2 achieved in solution increased to 14.3 mM from 10.8 mM with the monometallic catalyst. With higher platinum amount the initial selectivity was lower, but in all these catalysts the addition of platinum limited the decrease of selectivity with time in comparison with the monometallic one. The addition of platinum in increasing amount seems also to favour poisoning of the catalysts by the products (most likely by H2O2). The presence of small amount of gold is also effective in achieving a comparatively high initial selectivity. With the addition of only 0.25% Au (w/w), the initial selectivity towards H2O2 and the top concentration of the product were boosted up to 61% and 17 mM, respectively. Gold in relatively little amount is also useful to limit the decrease of selectivity with time. In particular, it seems to limit the combustion of hydrogen and to be much more effective than platinum in this respect. Preliminary TEM analysis of the size and size distribution of the metal nanoparticles in the Au-Pd bimetallic catalysts shows that relatively large nanoparticles are preferable to achieve higher and stable selectivity, but also that size is likely not the most important parameter in controlling the catalyst performance.

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Keywords
H2O2 direct synthesis; Palladium; Pd-Pt; Pd-Au; Lewatit K2621; Absence of promoters
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Pd-Au and Pd-Pt catalysts for the direct synthesis of hydrogen peroxide in absence of selectivity enhancers
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 468, 5 November 2013, Pages 160–174
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
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Don't Miss Today's Special Offer
Price was $35.95
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Price after discount Only $4.95
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